A drill bit is a cutting tool for “drilling” a hole in a work piece made of a variety of materials, such as wood, metal, plastic, and alloys. In general, it is difficult to drill multiple holes in hard material, such as a high-strength alloy, particularly when the cutting edges of the drill bit become ineffective as the drill bit is dulled by repeated use caused by the abrasive properties of the hard material. Diamond coatings applied to the cutting edges of a drill bit have overcome some of the problems associated with drilling hard materials. However, diamond coatings on the drill bit often separates from the drill bit material (serving as substrate for the coating) after intensive and continuous use. A useful, although comparatively expensive, coating is a polycrystalline diamond (PCD) coating that is applied by brazing. To reduce cost other methods of applying diamond containing coatings are often used. However, some of the other methods of applying diamond coatings have problems with coating/substrate separation.
The structure of a conventional drill bit 10 is depicted in FIG. 1. The cutting edges of the bit are on the forward end of the bit and are adjacent to the chisel edge of the bit. As the drill bit rotates cutting edges remove material from a work piece to form a hole. Because the drill bit surface, such as a diamond coating, is harder than the material of the work piece, the rotating cutting edges remove the softer material of the work piece. The pieces of material resulting from the removal process are transferred beyond the cutting edges of the drill bit via grooves in the drill bit.
In general, materials for drill bits are made of high-speed steel or tungsten carbide (CW). The front portion of the body of the drill bit that receives a coating, such as a diamond coating, is sometimes referred to as a substrate. When a harder material is applied to the substrate, such as a diamond coating, the drill bit performance is usually improved. Although the material typically used to form the body of a drill bit has excellent toughness, such materials frequently have poor wear resistance when used to machine hard materials, such as A390 alloys. It is generally known that there are several coatings, such as, carbide coatings and diamond coatings, that have excellent in wear resistance when bonded or otherwise applied to the drill bit substrate. However, some coatings may be brittle or may separate from the substrate due to drill bit manufacturing limitations. There is need to improve the coating process so that drill bit performance is improved.